The invention relates to a method for increasing the availability of a hybrid separating clutch in a hybrid drive train of a motor vehicle, in which the hybrid separating clutch is arranged between an internal combustion engine and an electric traction drive.
A method is known from EP 1 497 151 B1 for operating a motor vehicle with a drive engine and a transmission in the drive train. Here, a separating clutch is arranged between the drive engine and the transmission, which is actuated by a hydrostatic actuator. The hydrostatic actuator here allows the torque transmission to be carried out by the separating clutch. The control of the hydrostatic actuator occurs via a control unit, which comprises a control and power electronic controlling the drive motor of the actuator, for example an electric motor. In order to address the separating clutch the drive device is connected to additional sensors, with furthermore signal connections to other electronic units being provided, for example a superimposed control device such as a motor electronic, an anti-lock braking system, or a traction control.
When such a separating clutch actuated by a hydrostatic actuator is used in a hybrid drive system, it is arranged between the internal combustion engine and an electric traction drive. The electric traction drive is here used to set the hybrid vehicle in motion without using the internal combustion engine. When driving with the internal combustion engine the torque can be increased with an electric motor of the electric traction drive by the electric motor being operated in a motorized fashion. The electric motor may also be used to charge a battery in the generator mode and to operate the internal combustion engine in a range with higher effectiveness.
The hydrostatic actuator is self-locking for pressures of a hydraulic medium up to approximately 25 bars. This means that electrically no energy needs to be applied to hold the system in its actuated position because the pressure in this hydraulic system is usually below this threshold. In case of a failure of the hydrostatic actuator the clutch remains in its previous position so that situations may develop in which a continued driving with the hybrid vehicle is no longer possible.